This invention relates generally to voltage measuring circuits and, more particularly, to a voltage measuring circuit with an expanded scale.
In many instances an observer is interested only in the magnitude of a voltage existing between certain known limits well above zero and would like to easily determine values within those limits without the requirement for an excessively large meter. For these reasons circuits commonly known as expanded scale meter circuits have been developed. In the usual electrical indicating meter or instrument, there are a definite number of parts per division throughout the range or length of the scale for a given measured quantity. With an expanded scale circuit or meter, a certain portion of the measured quantity is selected and indicated on the meter with the same number of parts per division over the scale length, thereby providing higher readability of that selected portion than is possible without the scale expansion.
Known expanded scale devices include some employing highly complex circuitry and others that obtain expansion by mechanically suppressing an indicator at near zero voltage values. Also known is the use of a constant voltage device such as a gaseous discharge tube in series with a meter. Although extremely simple, this latter arrangement does not offer the accuracy needed in many applications.
The object of this invention, therefore, is to provide a relatively simple, low cost expanded scale instrument that exhibits a high degree of measuring accuracy in a specific range of interest.